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Old 27th September 2011, 01:50 AM   #1
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Default New to LTspice, need help, please.

I'm stuck with LTSpice, new to it, trying to learn-it with a project.
Attached is a real life working amplifier "Crescendo" from the Elector review. I believe my schematic is good as i cannot find any error.
But it shows DC F...-up.
So i suppose my models for transistors or fets are not correct. Can-you, please, help-me to make this amplifier working in LTspice, for i can propose to the community a nice improvement of it in the next future with a project i would like to realise.

You can ask-me for any other element you will need. Attached, the ".asc" and '.net' files.
http://www.esperado.fr/temp/Aymetric...n-Feedback.asc
http://www.esperado.fr/temp/Aymetric...n-Feedback.net

Thousand thanks in advance.
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Old 27th September 2011, 04:05 AM   #2
jcx is offline jcx  United States
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feedback R11 should be kOhms?

I would "zero" all ps, Vref bypass C by editing their multipliers to f (femto) - otherwise long RC time constants can make DC solver errors take seconds of sim time to decay

to share a sim with 3rd party device models the simplest is to just put the models directly on the schematic with the .op "spice directive" cmd
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Old 27th September 2011, 07:02 AM   #3
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Quote:
Originally Posted by jcx View Post
feedback R11 should be kOhms?

I would "zero" all ps, Vref bypass C by editing their multipliers to f (femto) - otherwise long RC time constants can make DC solver errors take seconds of sim time to decay

to share a sim with 3rd party device models the simplest is to just put the models directly on the schematic with the .op "spice directive" cmd
First, thanks for your nice answer JCX.
Yes, R11, corrected. But the problem did not comes from there. Still the same: -64V in the output..
I'm sorry, but i had not understood your following remarks. As i says, i'm brand new at those Spice programs, and this one looks to me like a miss. So fee warnings, no tool to edit models from the manufacturers data sheets, quasi no models delivered with it, and a very confusing and not ergonomic interface (to my taste).
So, i imagine you have to explain-me the things like to a baby ;-)
And no French translations of the help file do not makes the things easy for me, English is not my native language...
Error log said a lot of things i do not understand neither (i feel stupid):

Circuit: * E:\Program Files (x86)\LTC\LTspiceIV\Aymetrical-Input-tension-Feedback.asc
WARNING: Node N021 is floating.
Instance "m4": Length shorter than recommended for a level 1 MOSFET.
Instance "m3": Length shorter than recommended for a level 1 MOSFET.
Instance "m2": Length shorter than recommended for a level 1 MOSFET.
Instance "m1": Length shorter than recommended for a level 1 MOSFET.
Early termination of direct N-R iteration.
Direct Newton iteration failed to find .op point. (Use ".option noopiter" to skip.)
Starting Gmin stepping
Gmin = 10
Gmin = 1.07374
Gmin = 0.115292
Gmin = 0.0123794
Gmin = 0.00132923
Gmin = 0.000142725
Gmin = 1.5325e-005
Gmin = 1.6455e-006
Gmin = 1.76685e-007
Gmin = 1.89714e-008
Gmin = 2.03704e-009
Gmin = 2.18725e-010
Gmin = 2.34854e-011
Gmin = 2.52173e-012
Gmin = 2.70769e-013
Gmin = 0
Gmin stepping succeeded in finding the operating point.


Date: Tue Sep 27 09:00:32 2011
Total elapsed time: 0.120 seconds.

tnom = 27
temp = 27
method = modified trap
totiter = 2542
traniter = 2090
tranpoints = 1046
accept = 1046
rejected = 0
matrix size = 91
fillins = 209
solver = Normal
Matrix Compiler1: 20,5 Ko object code size 3.1/1.5/[1.1]
Matrix Compiler2: 11,5 Ko object code size 1.1/1.1/[0.7]
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Last edited by Esperado; 27th September 2011 at 07:16 AM.
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Old 27th September 2011, 11:21 AM   #4
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Updated schematic with models on it, as requested. Please, i really need help.
http://www.esperado.fr/temp/Asymetri...n-Feedback.asc
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Old 27th September 2011, 11:58 AM   #5
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Esperado,
The two P channel mosfets are upside down, and this is why it's stuck at the negative rail.
I suggest you start with a really simple circuit, with ideal current sources for the input long tail pairs, and an ideal voltage source to set the output mosfet bias. When you have it working properly, then replace the ideal current sources etc with the actual circuit. This makes fault finding much easier.
Paul Bysouth
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Old 27th September 2011, 12:32 PM   #6
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Quote:
Originally Posted by PaulBysouth View Post
Esperado, The two P channel mosfets are upside down,
You saved my life, thanks a lot for your help and care, Paul.
It works wonderfully now. Can 20 years away from electronic explain such a stupid mistake on my side ?
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